As one can notice from the title, there is no burning big brother, the only thing that burns is the main character's soul because of too much honor, fighting spirit and wisdom. The premise of the anime is very simple, Kenichi (a guy who knows martial arts and lived till 15 years of age in the wilderness) returns home to a loving family consisting of the father Kenji, sister Yukie and brother Kenkichi. From here on, the fun starts because the viewer will be bombarded with insanity and comical events from the daily life of the family. Typical of 80s style comedies but if the potential watcherdoesn't know, let's put it this way:
- It has characters screaming and punching each other because of mundane happenings
- People randomly transforming into chibi versions
- Horrible puns where only a japanese will laugh
- Explosions

When compared with modern popular comedies, I'd say it resembles Danshi Koukousei no Nichijou and Asobi Asobase, same style of explosive comedy and weirdness in a high school setting with surreal events happening here and there. And like those two, Oniisan never fails to deliver amusement each episode managing to stay fresh every time.

The structure of the show is episodic, one can watch this anime is reverse order or shuffle it and it won't matter. It was made for laughs and joy, live in the moment, the only plot that matters is what crazy thing will the gang do this time, especially Kenichi.
The romantic subplots are also played for laughs, you can juggle and invent ships in your head but it'll be useless.
A vital point to understand this anime is that the overall joke is how a wild Kenichi reacts to civilized life therefore all episodes will have scenarios that emphasize that. For example:
- Kenichi has to go to school, how will he behave?
- Kenichi has to go to the supermarket, can he manage buying rice?
- Kenichi discovers NES games
All of this will result in comical situations and slapstick

Most important element of this show is the characters, without them acting in a certain personalized way, we wouldn't get so much fun, in this case the anime nailed it, each one's behavior to issues creating comedy.
Kenichi is a kind boy but his wild side interferes too much in this urban life creating problems in his family, has the same IQ as Hanabatake Yoshiko
Yukie is a cute and caring girl
Kenji (the father) is the typical sour individual, revengeful small and petty
Kenkichi is the little brother who respects Kenichi a lot but he's almost as shrewd as his dad in some situations
Kaede is the hot beauty who lived as Kenichi's adopted sister in the wild, she plays 2nd fiddle in the anime, while having the same upbringing in the wild, she will also have to adapt to city life and comedy will happen around her too.
Ojisan is Kenichi and Kaede's adopted father, he's the true "villain" of this anime, every time he appears he creates chaos and absolute mayhem while having a stern look, he's more of a deadpan comedy character
There are other stereotypical characters in the anime and they do a good job for their worth, they interact well with the main cast and create funny events.

The VAs did a great job portraying them, all sound as annoying as they should when they behave like idiots, Yukie and Kaede are damn right cute. To make yourself an image, Kenichi is voiced by Franky from One Piece.
The OST is not that impressive but it manages to fill in and creates an atmosphere, it's not the type of show that demands cool music anyways, what it matters is that one moneymaker scene that is supposed to make the viewer laugh and the direction uses the OST the right way.

A small problem may be the art style which is a bit dated because of its simple approach. Most of the time the background is the usual urban view (inside house, city streets, school, shops) while the characters are drawn undetailed.
Cool sakuga is used in important scenes, you will notice great animation at least once per episode, those explosions and random running have to look good.
The art shines when the comedy scenes appear, as in the facial expressions will be done meticulously and detailed, the staff invested time and energy when it counts and the viewer will certainly notice that, not one comical event is half-assed. Now if the potential watcher is a fan of this type of Aho Girl-like humor is another story. This was made for people who love nonsensical and bombastic comedies, looking appealing was a second thought and lots of people will run away because of the ugly designs.

All in all, Moeru Oniisan managed to be a funny comedy for the audience they had in mind, it has all the pieces to please explosive slice of life comedy lovers. To describe it in one sentence, It's an anime about a muscular teen Mowgli with the IQ of a monkey getting to live in Tokyo alongside Yorozuya.